1. Field of the Invention
This invention relates to bent optical fibers, to optical systems such as optical amplifiers incorporating such fibers and, to a method of assembling such optical systems.
2. Technical Background
It is well known, throughout the photonics industry, that insertion loss due to macrobending in single-mode fiber increases with smaller radius of curvature and with longer wavelength of the transmitted light. This knowledge has led to standard practices for the deployment of optical fiber in spliced concatenations of pigtailed components such as Erbium doped fiber amplifiers (EDFAs) and Multiplexing/Demultiplexing assemblies. Macrobending is typically controlled in the design of optical systems by ensuring that the fiber is bend around large radii such as 25 mm or greater. This approach, however, works in direct opposition to the requirement of reducing the size of the optical systems. Furthermore, the macrobend losses become larger when the signal wavelength is longer, which is required in long-band (L-band) amplifiers. A long band amplifier is an amplifier that operates in an approximately 1560 nm to approximately 1625 nm wavelength range. Sometimes the bent optical pigtails are utilized in optical systems that operate at even longer wavelengths, for example about 1650 nm.
As we seek to reduce the overall size of optical systems comprising concatenated optical components, we need to be able to bend or coil the pigtails more tightly and simultaneously avoid increase in bend losses.
According to one aspect of the present invention a method of assembling an optical system includes the steps of:
(i) selecting, from a plurality of optical fibers characterized by a common nominal cut-off wavelength xcexcn and an actual cut-off wavelength xcexc such that the cut-off wavelength xcexc of each one of this plurality of fibers is the same as the nominal cut-off wavelength xcexcn or differs slightly from the nominal cut-off wavelength due to manufacturing tolerances, only fibers with xcexc greater than xcexmin, where xcexmin is a predetermined minimum acceptable cut-off wavelength of the selected fibers; and
(ii) bending at least one section of at least one of these selected fibers such that this bent section has a bend radius R, where 12 mm less than R less than 18 mm.
According to one embodiment of the present invention, the method of assembling an optical amplifier comprises the steps of: (i) manufacturing a plurality of optical fibers, the fibers being single-mode fibers that have a common nominal cut-off wavelength xcexcnxe2x89xa71290 nm; (ii) and bending at least one section of at least one of these fibers such that this bent section has a bend radius R, where 12 mm less than R less than 18 mm.
According to an embodiment of the present invention an optical system is selected from at least 10 optical systems which are identical except for differences due to manufacturing tolerances. Each of these optical systems includes bent optical fiber pigtails having: (i) a bend radius R, such that 12 mm less than R less than 18 mm; (ii) a common design cut-off wavelength xcexcn, and (iii) an actual cut-off wavelength xcexc, such that the cut-off wavelength xcexc of each of the optical fibers of these pigtails is larger than the same or larger than xcexcnxe2x88x921.5 xcex94, where xcex94 is a standard deviation of xcexc distribution.
According to an embodiment of the present invention, a method of assembling an optical amplifier comprises the steps of:
(i) manufacturing a plurality of optical fibers, the optical fibers being single-mode fibers that are characterized by a common nominal Mac number MACn, such that the Mac number MAC of each of the optical fibers is the same as the nominal Mac number MACn or differs slightly from the nominal Mac number due to manufacturing tolerances;
(ii) selecting from these optical fibers only fibers that satisfy the following equation MAC less than MACn+xcex94, where xcex94 is a standard deviation of Mac number distribution of said plurality of optical fibers; and
(iii) bending at least one section of at least one of these selected fibers such that this bent section has a bend radius R, where 12 mm less than R less than 18 mm.
According to an embodiment of the present invention a method of assembling an optical amplifier comprises the steps of: (i) selecting from a plurality of optical fibers only fibers that satisfy the following equation MAC less than 7.0, where MAC is a Mac number of each of the selected fibers; the plurality of optical fibers being single-mode fibers; (ii) and bending at least one section of at least one of the selected fibers such that this bent section has a bend radius R, where 12 mm less than R less than 18 mm.
According to one embodiment of the present invention an optical system selected from at least 10 optical systems which are identical except for differences due to manufacturing tolerances, each of the optical systems including optical fiber pigtails having: (i) a bend radius R, such that 12 mm less than R less than 18 mm; (ii) a common design Mac number MACn; and (iii) an actual Mac number MAC, such that the actual Mac number MAC of each of the fibers is the same or smaller than said common design Mac number MACn.
It is an advantage of this invention that optical amplifiers and other optical devices of the present invention can utilize strongly bent optical fiber (with bend radius of 12 to 18 mm) without suffering from extensive macrobend losses and, thus, can be more compact and operate at longer wavelengths.
For a more complete understanding of the invention, its objects and advantages refer to the following specification and to the accompanying drawings. Additional features and advantages of the invention are set forth in the detailed description, which follows.
It should be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various features and embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.